1. Field of the Invention
The invention pertains to electronic means for generating an early and easily assimilable warning of the build-up of an unacceptable traffic conflict in a harbor or estuary or in other confined waters viewed by a shore-based traffic surveillance system and more particularly relates to means for the computer generation of a graphic display adaptable for use with such surface search radar systems for the purpose, in the first instance, of determining the degree of conflict or of safety of monitored vessels with respect to established operational criteria. Secondly, the invention provides a quickly and accurately interpretable display for assessing the optimum effective procedures for elimination of the hazard condition and, furthermore, generates a permanent printed data record both in tabular and graphical formats.
2. Description of the Prior Art
Radio, radar, and other sensor systems have been employed in the past for communication and for surveillance and monitoring of marine traffic from a shore-based station or stations in the approaches and environs of ports, rivers, and harbors for improving safety of passage and orderly scheduling of movement of shipping. The technology is based upon exploitation of direct visual observation and radar sensing techniques and upon procedures developed for collision avoidance of mobile craft and vessels on the high seas and in waters connected therewith.
Typically, such harbor surveillance systems consist of one or more shore-based azimuth scanning radar systems, supported in the plural configuration by broad-band data linking systems such as microwave relay links or co-axial cable where ever the radar data from a multiplicity of sensors is to be viewed at a single control or operational surveillance center. The marine traffic pattern is viewed at one or more shore-based radar plan position indicators by operators whose function is to interpret the traffic situation and to generate alerts when unacceptable ship movements occur or more importantly are about to occur, and to communicate with and to receive communications from ships within their spheres of coverage, such communications being concerned with the identification of specific ships in relation to their present positions and future maneuver intentions. In the special conditions where ships lack and are unable to acquire information necessary to their safe navigation, the operators provide such information in a form intelligible to and convenient to the shipmaster or pilot on board the cooperating vessel. A specific function of the shore-based radar surveillance system is to provide information which is available to the shore station by virtue of the selected location of its radar sensors and which may not therefore be available by examination of similar radar equipment on a specifically located ship because of restricted radar coverage in land-locked constricted canals, rivers, or narrow estuaries.
Recent concern with the promotion of improved safety of marine operations for the purposes of environmental protection and preservation has also added encouragement to governmental agencies of the leading nations to promote legislation governing the establishment and efficient operation of maritime traffic surveillance systems. Initially, such systems will monitor traffic and issue advisory communications to voluntarily participating vessels. It can be expected that vessel participation will become mandatory.
Even though shore-based surveillance systems may possess advantages over shipborne equipments devoted to acquiring navigational and traffic information by reason of their carefully-planned deployment and of the deliberate sophistication of equipment matched to high orders of reliability and availability and supported by application of the accurate and rapid data processing capability of the digital computer, certain impediments occur. The individual vessel negotiating an area of difficulty in terms of navigation or traffic density may exercise some discretion in applying its available resources to address those problems of most immediate concern and consequence. In contrast, the shore-based surveillance system must perform its functions with respect to its total surveillance region. When traffic densities are high, the work load generated is known to reach overwhelming levels. The combination of all of the threats posed by encounters of all the traffic elements taken a pair at the time can reach high numerical values.
More recent shipboard collision threat assessment techniques use automatic target trackers to acquire radar target data and a digital computer to process the radar target data and to provide easily-assimulated presentations of collision threat information to the shipmaster. Efforts to exploit these techniques at the shore-based location have revealed severe limitations. In shipboard systems designed to cope with the pattern of encounters which occur in the open sea, it has been discovered that a more limited applicability results in situations where ships are forced to abandon their normal operating pattern, which is to proceed in general on steady courses with steady speed and to follow the sometimes torturous channels of an estuary or harbor. In the latter situations, the likelihood of the ship continuing on at least a steady course is curtailed severely. Reliance upon the convention of prediction of future events based upon the extrapolation of the present positions, speeds, and courses of vessels becomes impossible. Instead, reliance is based on the convention that vessels will follow a predicted set of courses and speeds and normal radar displays are therefore used to monitor the situation to see that the ships do in fact follow the predicted courses. This allows prediction of the vessels' future positions even in the usual situation in which a number of bends or changes in channel configuration intervene.